HTML is the basic language used in web pages. It is designed to run in different browsers and on different operating systems. It consists of a list of instructions that tell the browser how to render the page i.e. text size and colour, where to place graphic images etc.
This is the most widely used language for web sites and is adequate where there's a requirement to display fixed information. There are many languages used on the web but whatever is used, ultimately the outcome is always HTML displayed in the browser.
HTML is NOT a programming language; it's a Mark-up language. This is a set of instructions that describe how a document is to be structured, laid out, or formatted.
Generally these instructions are carried out in the order in which they are listed and will always produce the same result each time the web page is displayed.
A programming language, on the other hand, is a list of instructions that normally contains conditional statements, i.e. statements that alter the order in which instructions are to be carried out depending on set conditions.
This means that a programming language will produce different results each time the conditions set are altered. Examples of programming languages are JavaScript and PHP.
HTML began life as a simple language to allow non-programmers to produce web documents but gradual revisions, prompted by additional requirements, have made the language much more complex.
If simple documents are required then the novice will find basic HTML straightforward. If more complex documents are required then more time and thought is needed.